Hitherto, as disclosed in, for example, Patent Literature 1, there has been a method involving, when a metal and an unvulcanized rubber are bonded to each other through an adhesive, applying a pressure, with heating, to the adhesive to vulcanize the rubber, to thereby bond the rubber and the metal to each other.
In such bonding method, first, it is necessary to apply a solvent dispersed type vulcanization adhesive to the surface of a metal with a brush, a spray, or the like. As used herein, the term “solvent dispersed type vulcanization adhesive” refers to a polymer compound having adhesiveness in which a filler, a cross-linking agent, a stabilizer, and the like are dispersed or dissolved in an organic mixed solvent. In this operation, a volatile organic compound (hereinafter referred to as “VOC”) is used as a solvent for the adhesive. In recent years, in consideration of the health of workers and the environment, it has been necessary to suppress the emission amount of the VOC, and each operator has been required to voluntarily reduce the emission amount of the VOC, in addition to the emission constraint by the law and the administrative guidance. Thus, in a working area for performing bonding, specific means for suppressing the emission amount of the VOC is necessary. In order to suppress the emission amount of the VOC, it is necessary to improve the working environment including a facility and a place. However, when the working environment is improved in a working area for performing bonding, the scale of the working area becomes larger. Further, it is necessary to thinly apply the solvent dispersed type vulcanization adhesive. However, when an attempt is made to form a thin applied layer of the adhesive with a brush, a spray, or the like, it is difficult to manage the film thickness so that the film thickness may become uniform. Further, there have been problems in that the coating efficiency is unsatisfactory, and the amount of the adhesive that dissipates without being applied to the surface of the metal increases.
In view of the foregoing, in Patent Literature 2, there is a disclosure of an adhesive sheet configured to bond an unvulcanized rubber to a metal, the sheet including: a release film made of a polymer compound; an upper adhesive layer obtained by applying a solvent dispersed type vulcanization adhesive having reactivity with the rubber onto one surface of the release film and drying the solvent dispersed type vulcanization adhesive; and a lower adhesive layer obtained by applying, after drying the upper adhesive layer, an adhesive having reactivity with the metal onto a surface of the upper adhesive layer on an opposite side of the release film and drying the adhesive.
This adhesive sheet serves to bond the rubber to the metal as described below. A metal to be bonded to a rubber is set, and a surface of the lower adhesive layer of the adhesive sheet on an opposite side of the upper adhesive layer is pressed against the metal to be fixed to an upper surface of the metal. In this state, a rubber mat is placed on the release film, and the metal is heated while a pressure is uniformly applied to the rubber mat. Then, after the lower adhesive layer is firmly fixed to the metal, the release film of the adhesive sheet is removed from the upper adhesive layer. A pressure is applied, with heating, to the unvulcanized rubber on a surface from which the release film has been removed, to thereby vulcanize the unvulcanized rubber and firmly fix the upper adhesive layer and the rubber to each other. In this adhesive sheet, the VOC is removed in advance in a manufacturing stage of the adhesive sheet, and hence there is an advantage in that the amount of the VOC at a time of the bonding of the rubber to the metal can be reduced.